import pandas as pd
df_missing = pd.DataFrame({'A': [1, None, 3], 'B': [None, 5, 6]})
print(df_missing.isnull())       # 检测缺失值
print('-'*35)
print(df_missing.fillna(0))      # 用0填充缺失值
print('-'*35)
print(df_missing.dropna())      # 删除包含缺失值的行
